1. Technical Field
This invention relates to an oil ring assembly for an internal combustion engine piston.
2. Prior Art
U.S. Pat. No. 2,848,288 issued Aug. 19, 1958 to R. H. Johnson on a piston ring shows an oil ring assembly including a ring formed from a blank which is flat except for a reduced thickness area in the middle. After being bent to a desired shape and installed in a piston, the ring provides a pair of concave shoulders engaged by the coils of the expander ring. The coils of the expander ring do not engage the bottom of the trough formed by the reduced thickness area.
Section views of prior art oil ring assemblies are shown in FIGS. 5, 6, 7 and 8, in which the annular groove for the coiled expander spring includes circumferentially spaced slots. In the prior art construction shown in FIG. 5, the bottom 61 of the groove 62 is flat as viewed in section. During operation, the coils of the spring 63 tend to catch on the edges of the slots 64 thereby decreasing their effectiveness in biasing the ring 66. In the prior art shown in FIG. 6, the groove 72 in section is a part of a circle whose radius is greater than the radius of the coils of the expander spring 73. In this configuration, the coiled expander spring contacts the edges of the slots 74 causing excessively high loading. Also, the coils of the spring will catch on the end edges of the slots thereby decreasing the effectiveness of the coiled expander spring 73 in providing radially outward biasing force against the ring 76. In the prior art oil ring assembly shown in FIG. 7, the contact of the coils of the spring 83 with the tangential walls of the V-shaped groove 82 produces relatively high unit loading at the points of contact thereby tending to cause excessive wear. In the prior art construction of FIG. 8, the groove 92 for the expander spring 93 is formed by as bottom segment 95 having a radius less than the radius of the spring coils 93 by curved segments 96, 97 radially inward relative to the ring which have a radius larger than the coils of the expander spring 93 and by two conical surfaces 98, 99 (which are flat in the section view of FIG. 8) which are approximately tangential to the before-mentioned bottom and curved segments. Thus, the coils of the spring 93 bear against flat tapered sides of the groove 92 in somewhat the same manner as in the prior art design of FIG. 7 with the attendant high unit loading at the contact points between the spring coils and the groove surface.